Automatic volume control



oet 8, 1946. H. M. s TEARNs y 2,408,821

` AUTOMATIC VOLUME CONTROL original Filed July so, 1942 TE/VS ATTORNEY Patented Oct. 8, 1946 AUTOMATIC VOLUME CONTROL Horace Myrl Stearns, Merrick, N. Y., assignor to Sperry Gryoscope Company, Inc., Brooklyn, N. Y., a corporation of New Yorky Original application July 30, 1942, Serial No.

Divided and this application November 6, 1943, Serial No. 509,225

(Cl. Z50-20) 16 Claims.

This invention relates to automatic volume control for radio receivers. Although the invention is generally useful in all types of radio and other signal receivers, it is described herein as applied to a pulse receiver for a radio detection system such as that shown in copending application Serial No. 452,818, filed July 30, 1942, in the names of Eric J. Isbister, Horace Myrl Stearns, and Walter N. Dean, of which the present application is a division.

An object of the invention is to provide an automatic volume control circuit for controlling the potential applied to the screen grids of amplifying tubes in a receiver to adjust the amplification of the receiver and thus to stabilize its output.

A further object of the invention is to provide an automatic volume control circuit for controlling a high potential, high current source supplying energy to the screen grids of amplifying tubes in a receiver according to the average level of the receivers output.

A still further object of the invention is to provide an automatic volume control :circuit which uses the average output level of a receiver to control a source of high potential applied to the screen grids of amplifying tubes in a receiver in a manner to maintain the output of the receiver at a substantially constant level.

Other objects and advantages of the invention will become apparent from the following specilication, taken in connection with the accompanying drawing which shows a schematic diagram of a radio receiver employing an automatic volume control circuit embodying the invention in its preferred form.

It has previously been proposed to control the screen grid of an amplifying tube according to the output of a radio receiver in a manner to maintain the output at a more or less constant level. However, difficulties have been encountered, since the screen grid of an amplifying tube demands a substantial amount of current at a relatively high potential.

According to the present invention in its preferred form, the screen grids of amplifying tubes in several stages of the intermediate frequency amplier of a radio receiver are supplied with a voltage of a suitable potential that may be adjusted according to the average output level of the receiver in a manner to stabilize the output level. An automatic volume control circuit embodying the invention permits a small change in the output level to be applied to several screen grids in the intermediate .frequency amplifier stages to produce an overall change in the amplication of the receiver that is adequate to maintain the output level substantially constant.

Since the potential applied to several screen grids is to be controlled, the current supplied by the source must be comparatively large. The voltage applied to the screen grids of these tubes may be readily adjusted by changing the resistance connected in series with the screen grids. According to the present invention in its preferred form, a variable resistance in the form of a power tube is placed in series with the voltage supply for the screen grids of the amplifying tubes in several stages of the intermediate frequency amplier. The resistance of this power tube is adjusted according to the average output level of the receiver. To effect this adjustment, the power tube is arranged in series with a high gain control tube and a suitable impedance.

A voltage corresponding to the average output level ofthe receiver is applied to the control grid of the high gain control tube. This varies the current drawn by the control tube through the power tube and impedance according to the outpu+u of the receiver, although variations in the current through the power tube are comparatively small. The voltage drop across the impedance connected between the two tubes is used to control the bias applied to the grid of the power tube. Since this drop varies according to the current drawn by the control tube, it corresponds to the output level of the receiver; the resistance of the power tube is therefore also changed as the output level of the receiver varies.

As the resistance of the power tube varies, the drop across it due mainly to the current drawn by the screen grids of the amplifying stages also varies according Vto the output level of the receiver. The circuits are so arranged that an increase in the output intensity of the receiver increases the resistance of the power tube, thereby reducing the voltage applied to the screen grids of the amplifying tubes and thus reducing the overall amplication of the receiver to maintain its output level substantially constant.

Referring to the drawing, which shows a pulse receiver for a radio detection system, pulses of electromagnetic energy are collected by an antenne, I I. As is `well known in such detection systems, an object or tar-get is irradiated by short, sharp pulses of electromagnetic energy and the reflected pulses are used to detect the presence and position of the object.

APulses of electromagnetic energy collected by the antenna I I aresupplied to a conventional frequency converter I2, which may be a high frequency superheterodyne mixer including a suitable local oscillator to produce the usual intermediate frequency wave. The intermediate frequency signal, modulated in this case by the received pulses, is supplied through a-coupling condenser IS across a grid resistor I4 to control grid It of an amplifying tube I8 shown as a pentode connected in a conventional amplier circuit designated by the numeral I9. This circuit forms the first stage of an intermediate frequency amplifier in the receiver. Plate 2I of the tubeV I8 is connected through load resistor 22 to a' suitable source 23 of positive potential, and cathode 24 is connected through a bias resistor 25 to ground. Screen grid 26 of tube I 8 is connected by a lead 23 to a separate source of potential which is controlled by the automatic volume control circuit embodying the present invention.

The output voltage of the rst stage I9 is cou- .ventional wide band amplier 34 designed to maintain the Wave shape of received pulses.

The received pulses are also accompanied by interspersed stray noise Waves and other undesired pulses, due to multiple reflections or further reflecting objects, which might impair the desired indications, In order to reduce the effect of such interspersed noise and stray pulses the received Wave from the wide band amplifier 34 is transmitted through a pulse gate 36 which is adapted, as will be described, to permit only the passage of the desired received pulses while effectively blocking or wiping out such extraneous noise and stray pulses. Pulse gate 36 is placed under the control of a pulse generator 38 which is adapted to produce a sequence of pulses having the same frequency or repetition rate as, and a duration substantially the same as or slightly longer than, the received pulses. The time phase of the generated pulses is made adjustable with respect to the phase of the received pulses under the control of a suitable manual control adapted to be actuated by the operator. Pulse gate 36, as will be described, comprises a normally blocked circuit which becomes unblocked only under the iniiuence of the generated pulses. By suitably adjusting the phase of the generated pulses to ,coincide with that of desired received pulses, the

desired received pulses may be transmitted to suitable indicating and control circuits While eliminating all undesired interspersed pulses and noise Waves.

The pulse gate 36 includes a control voltage derived from control oscillator 39 that is conducted to an adjustable phase shifter 4I of any conventional type, Whose phase shift is adapted to be controlled by manual control knob 42, This voltage Wave is supplied to a suitable square wave generator 43 and thence to the pulse generator 38. It will be clear that, by suitable adjustment of phase shifter 4I, the phase of the square wave output of generator 43 and of the pulses of generator 38 may be suitably adjusted with respect to that of control oscillator 39 ras desired. The duration of the generated pulses is preferably substantially equal to that of the received pulses or slightly longer. The generated pulses are fed by Way of a suitable coupling condenser 44 and coupling resistor 45 to the control grid of blocking amplier tube 46 whose cathode 4l' is connected to a source of fairly high negative voltage indicated schematically as 48, and Whose anode 49 is connected to ground through output resistor 5I. The screen grid of tube 46 is connected directly to ground. In this manner tube 46 is rendered normally conductive, and the generated pulses from the pulse generator 38 are adjusted to be of such magnitude and polarity as to interrupt the conduction of tube 46 for the duration of these pulses.

Theungrounded terminal of resistor '5I is also connected directly to anode 52 of a further blocking amplier tube 53 of the pulse gate 36, whose control grid 56 is energized by the receiver output Wave derived from the Wide-band amplifier 34 and connected to the control grid through a coupling condenser 58 and grid resistor 59. Cathode e I' of the tube 53 is connected to a source of fairly high negative voltage, which may be the same as source 48. Tube 53 is also rendered normally conductive, its conductivity being decreased in response to the pulses existing in the received Wave input that is applied thereto.

Resistor 5I is included in the input circuit of an amplifier tube 63 whose anode 64 is connected directly to a source 65 of high positive potential and whose cathode 66 is connected to a source 61 of low negative biasing potential through an output resistor 68 shunted by a condenser 69, Bias source 6'! may also be bypassed for alternating current by means of a by-pass condenser 'II.

In operation, in the absence of pulses applied to tube :i6 and tube 53, the normal quiescent current through resistor '5I from tubes 46 and 53 will produce a negative voltage thereacross suiiicient to overcome the bias of source 61 and to completely cut-off tube 63. Accordingly, zero output voltage will appear at the output of tube 63, which is.supplied by lead l2 to the ungrounded one or" a pair of terminals 13.

When a pulse from pulse generator 38 is impressed on blocking tube 46 it momentarily decreases the anode current of the tube 46 and accordingly decreases the voltage drop across resistor 5I, However, the circuit values are so selected that tube 63 is nevertheless still blocked in the absence of a corresponding simultaneous pulse from the received Wave impressed on blocking tube 53. When a pulse from pulse generator 33 is impressed on tube 46 simultaneously with a received pulse impressed on tube 53, the resultant decrease in current through resistor 5I is then suliicient to reduce the bias on tube 63 to a point where cathode current can iioW.

Accordingly, under these conditions a corresponding pulse will appear in the output which maybe connected from terminals 13 to any desired utilizing device. It will be seen that by adjusting the phase of the pulses from pulse generator 38, by means of manual adjustment 42, to be in phase coincidence with a desired received pulse, corresponding to a particular` reflecting object or target, an output Wave will be derived at terminals 'I3 corresponding to this reilected pulse, but this output will remain entirely unaffected by any other pulses or any accompanying noise Waves interspersed therebetween. The gate 36, therefore, acts to permit passage of a selected pulse determined by the setting of adjustment 42. Since these generated pulses are of very short duration, as described above, condenser 69 is provided across output resistor 68 of tube 63, of a capacitance adapted to substantially lengthen the pulses impressed on resistor 68. These lengthened output pulses represent the average output level of the receiver.

The lengthened output of pulse gate 36 is fed by a lead to an automatic volume control circuit which embodies the present invention.V The lengthened pulses are supplied by the lead 15 to a rectifier and lter circuit 16 to derive a voltage corresponding to the average intensity of the pulses transmitted by the pulse gate 36. This voltage corresponding to the average output of the receiver is then applied to control grid 8| of a high gain control tube 82 shown as a pentode whose cathode 83 is connected to a source 84 of low positive voltage providing a grid bias for the control grid 8| of the control tubev 82. Anode 85 of the control tube 82 is connected in series with a resistor 81 to cathode 88 of a power tube 89 shown in the drawing as a beam power tube. The anode 9i of the power tube 89 is connected to a source 92 of high positive voltage. The voltage drop across the resistor V81 is supplied to control grid 93 ofthe power tube 89 as by a lead 94.

In eiect, the output of rectifier unit 16 controls the conductivity and hence the internal resistance of the control tube 82. In this manner, the amount of current drawn from source 92 by the control tube 82 through the power tube 89 and the resistor 81 is controlled by the intensity of the receiver output represented by pulses from the pulse gate 38. Should this intensity vary so as to decrease the internal resistance of the control tube 82,.it will be clear that more current will now through the resistor 81 producing a larger bias on the control grid 93 of the power tube 89 tending to oppose this changing of current by increasingthe resistance of the power tube. Accordingly, the internal resistance of the power tube 89 will also change but in an opposite sense and an equilibrium condition will be reached once more. However, the potential of the cathode 38 of the power tube 89 will no longer be the same as before the change in intensity of the gated pulse. In the illustration used, the effective resistance of the control tube 82 was decreased and the effective resistance of the power tube 89 was increased. In this case, the potential of the cathode of the power tube 89 is lowered. It will be clear that an opposite change in pulse intensity will reverse the process and decrease the resistance of the power tube 89. In this way, the potential of the cathode of tube 89 will be changed according to the intensity of the i gated pulses.

In the circuit shown in the drawing, the cathode potential of the power tube is of a fairly high positive value and, accordingly, may be used directly to energize the screen grids of the intermediate frequency amplifier tubes.

For this purpose a lead 98 is connected from the cathode 88 of the power tube 89 to the lead 2S. which supplies potential to the screen grid 28 of the first stage and to a lead 99 which is connected similarly to the screen grids of the other stages of the intermediate frequency amplifier 32. f

The screen grids of the several amplifying stages draw a relatively large current constantly through the power tube 89 in addition to the current drawn by the control tube 82. The current drawn by the control tube 82 is relatively small and has little eiect on the potential drop across the power tube 89 but a larger effect on the drop across resistor 81. Hence, the grid bias of thev power tube 89,A as determined bythe voltage drop across the resistorA 81, varies aptY preciably to change the internal resistance of the power tube.

This change in the resistance of the power tube Yproduces a correspondingly appreciable change in the voltage drop across it because a relatively large current continuously flows through the power tube. Hence, the potential supplied to the screen grids of the amplifying tubes by the lead 98 changes sufficiently to change the amplification of the .various lintermediate frequency amplifier stages. By changing the amplication of all of the intermediate frequency amplifier tubes, a small change in the output level of the receiver may, by eifecting even a slight change in the voltage applied to the various screen grids, effect a sufficient overall change inthe amplification of the intermediate frequency amplifier to maintain the output of the receiver at a substantially constant level. Asis apparent from the foregoing description, control of the screen grids is accomplished by a voltage divider circuit, one portion of which supplies the high current that is drawn by the screen grids while another portion of the voltage divider draws a much smaller current but controls the resistance of the irst portion to change the amplification of the intermediate frequency amplifier.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An automatic volume control system for a signal receiver, comprising a voltage divider including a pair of electron discharge tubes arranged in a series circuit, means responsive to said receiver for oppositely changing the resistances of said tubes according to the average output level of said receiver, and means for controlling the amplification of said receiver according to the voltage across one of said tubes.

2. An automatic volume control system for a signal receiver including a screen grid amplier, comprising a voltage divider including a pair of electron discharge tubes arranged in a series circuit, means responsive to said receiver'for oppositely changing the resistances of said tubes according to the average output level of said receiver, and means for controlling the voltage of the screen grid of said amplifier according to the voltage across one of said tubes.

3. An automatic volume control system for a signal receiver, comprising a voltage divider including a pair of electron discharge tubes arranged in a series circuit, means responsive to said receiver for changing the resistance of one of said tubes according to the average output level of said receiver, means for oppositely changing the resistance of the other of said tubes, and means for controlling the amplification of said receiver according to the voltage across said other tube.

4. An automatic volume control system for a signal receiver, comprising a voltage divider including a pair of electron dischargetubes arranged in a series circuit with a resistor between said tubes, means responsive to said receiver for changing the resistance of one of said tubes according to the average output level of said receiver, means' for applying the voltage drop across said resistor to the other of said. -tubes to oppositely change the resistance thereof, and means for controlling the amplification of said receiver according to the voltage across one of said tubes.

5. An automatic volume control system for a signal receiver including a screen grid amplifier, comprising a voltage divider including a pair of electron discharge tubes arranged in a series circuit with a resistor between said tubes, means responsive to said receiver for changing the resistance of one of said tubes according to the average output level of said receiver, means for applying the voltage drop across said resistor to the other of said tubes for oppositely changing the resistance thereof, and means for controlling the voltage of the screen grid of said amplifier according to the voltage across said other tube for controlling the amplification of said amplifier to maintain the average output level of said receiver substantially constant.

6. An automatic volume control system for a receiver of radiant energy, said receiver including a screen grid amplifier for deriving therefrom the wave envelope of said energy, comprising means for producing a voltage corresponding to the average amplitude of said envelope, a divider comprising the series-connected anode'- cathode circuits of a pair of electron discharge tubes and a resistor connected therebetween, means for controlling the resistance of one of said anode-cathode circuits in accordance with said average voltage, means for controlling the resistance of the other of said anode-cathode circuits in accordance with the voltage drop across said resistor, and means for applying the Voltage drop across said resistor and said iirst anode-cathode circuit in series to the screen grid of said amplifier to control the amplification thereof, whereby said wave envelope is maintained substantially at constant amplitude.

'7. An automatic volume control circuit for a receiver of radiant energy, said receiver including a screen grid amplifier for deriving therefrom the wave envelope of said energy, comprising means for producing a voltage corresponding to the average amplitude of said wave envelope, a voltage divider comprising theseries-connected anode-cathode circuits of a pair of electron discharge tubes and a resistor connected therebetween, means for controlling the potential difference between said cathodes in accordance with said average voltage, and means for applying said potential diiierence to the screen grid of said amplifier to control the'amplication thereof, whereby said wave envelope is maintained substantially at constant amplitude.

8. In an automatic volume control circuit for a signal receiver, apparatus for producing a voltage dependent upon the average output level of said receiver comprising a; pair of electron discharge tubes arranged in a series circuit, and means responsive to saidl receiver forv oppositely changing the resistances of said tubesV according to the average output level of said receiver.

9. In an automatic volume control circuit for a signal receiver, apparatus for producing a voltage dependent upon the average output level of said receiver comprising a` pair of electron discharge tubes arranged in a series circuit; means responsive to said receiver for changing the reeistance ofone of said tubes accordingto'the average output level of said receiver, and means for 'oppositely changing the resistance of the other of said tubes.

10. In an automatic volume control circuit for a signal receiver, apparatus' for producing a. voltage dependent upon the average output level of said receiver comprisingv a pair of electron discharge tubes, a resistor arranged in a series circuit between said pair of tubes, means responsive to said receiver for changing the resistance of one of said tubes according to the average output level of said receiver, and means for applying the` Voltage across said resistor to oppositely change the resistance of the other of said tubes.

11. An automatic volume control system for a. signal receiver including a screen grid ampliiier, comprising a source of potential, a power tube forming a dropping resistor for connecting the screen grid of said ampliiier to said source of potential, and control means connected in series with said power tube and responsive to the average output level of the receiver for' controlling the resistance of said power tube to change the voltage applied to said screen grid in a manner to stabilize the output of said receiver.

l2. In an automatic' volume' control system for a signal receiver including a screen grid amplier, a source of potential, a power tube forming a dropping resistor for connecting the screen grid of said amplifier to said source, a control tube connected in series with said power tube, and means responsive'to the average output of said receiver for actuating said control tube'to change the resistance of said power tube thereby changing the voltage applied to said screen grid in a manner to maintain the output of said receiver substantially constant.

13. Anautomatic volume control system for a signal receiver, said receiver including an amplier having a plurality ofV screen grid amplifying tubes, comprising a source of potential, a power tube forming a dropping resistor for connecting the screen grids of said amplifying tubes to said source, and a control tube connected in series with said power tube and responsive to .the average output of said receiver for controlling the resistance of said power'tube thereby changing the voltage applied to said screen grids in a manner to stabilize said output.

14. In an automatic volume control circuit for a signal receiver, apparatus for producing a voltage dependent upon the average output level of said receiver comprising a source of potential, a power tube having its anode connected to said source, and means for changing the resistance of said tube to changethe potential of the cathode thereof according to changes in said output level, said means comprising a control tube connected in series with said power tube.

15. An automatic volume control system for a receiver of radiant energy, said receiver including an amplifier for deriving therefrom the wave envelope of said energy, comprising means'for producing a voltage corresponding to the average amplitude of said envelope, a divider` comprising the series-connected anode-cathode circuits of a pair of electron discharge tubes and a resistor connected therebetween, means for controlling the resistance of one of said anode-cathode circuits in accordance with said average voltage, means lfor controlling the resistance of the other of said anode-cathodecircuits inaccordance with the voltage drop across said resistor, and means for applyingthe voltage drop across said resistor cathode circuits of a pair of electron discharge tubes and a resistor connected therebetween, means for controlling the potential difference between said cathodes in accordance with said average voltage, and means for applying said potential difference to said amplier to control the amplification thereof, whereby said wave envelope is maintained substantially at constant amplitude.

HORACE MYRL STEARNS. 

